1. Field of the Invention
This invention pertains to electrodes for use in the air-carbon arc cutting and gouging process used in industry for cutting, cleaning, or preparing metals for subsequent fabrication operations. In the hands of a skilled operator, a ferrous material, e.g. steel plate, can be provided with a groove which can subsequently be filled with a weld metal deposit to effect a repair or facilitate a subsequent fabrication operation. The process can be automated and controlled to such a degree that grooves are provided or cuts made in metals that approach those machined or cut by conventional machine tools.
2. Description of the Prior Art
The air-carbon arc cutting and gouging process was first described in U.S. Pat. No. 2,706,236. According to the process as now practiced, a carbon (graphite) electrode, normally having a copper coating, is positioned so that an arc can be struck between the electrode and a work piece. At the same time the arc is initiated, compressed air is caused to flow down the side of the electrode following the direction of travel to forceably remove (blast away) molten metal produced by the effect of the electric arc.
Electrodes suitable for use in the air-carbon arc cutting and gouging process are discussed in detail in U.S. Pat. Nos. 3,030,544; 3,131,290; 3,566,069; 3,633,063; and 3,796,853. In all of the prior patents the conventional electrode for use in direct current (d.c. operation) is manufactured from a mixture of carbonaceous materials such as graphite, carbon black, a binder such as tar and pitch and if necessary, a lubricant. The mixture is mixed at an elevated temperature by a kneading technique and extruded to a finished cross-sectional shape which is then cut to length and baked at elevated temperature to provide a finished electrode substrate for use in the process. The finished electrode substrate is subjected to further surface finishing operations and then is provided with a copper coating to enhance conductivity when the electrode is used in a cutting or gouging operation.
Plain carbon or graphite electrodes have been used with alternating current (a.c.) power supplies in a conventional air-carbon arc cutting and gouging process. However, when such electrodes are used with an alternating current power supply the arc stability is very poor. Therefore, arc stabilizers such as mixtures of rare earth oxides have been used in the past to stabilize the arc. The conventional a.c. electrode is not satisfactory for d.c. operation and generally contains in excess of 30% by weight arc stabilizers. Conventional d.c. (plain carbon) air-carbon arc cutting and gouging electrodes operate at noise levels of between 120 to 120 dbA in normal use.